1. Field of the Invention
This invention relates to an optical recording medium, having a groove formed along a recording track, a master disc used for the preparation of the optical recording medium, and to an optical recording and/or reproducing apparatus for recording and/or reproducing information signals for an optical recording medium prepared using this master disc.
2. Description of Related Art
As an optical recording medium, an optical disc for optically recording and/or reproducing information signals is being practically used. Among such optical recording mediums, there are a replay-only optical disc having embossed pits corresponding to data, previously formed on a disc substrate, a magneto-optical disc for recording data by exploiting photomagnetic effects, and a phase-change optical disc for recording data by exploiting phase changes in a recording film.
Of these optical discs, those which permit writing, such as magneto-optical disc or phase-change optical disc, are usually formed with grooves extending along a recording track. By the groove herein is meant a so-called guide groove formed for extending along the recording track mainly in order to permit tracking servo. An area between neighboring grooves is termed a land.
In an optical disc, carrying these grooves, tracking servo is performed based on push-pull signals obtained from light reflected and diffracted by the grooves. The push-pull signals are obtained by detecting the light reflected and diffracted by the groove by two photodetectors, arranged symmetrically with respect to the track center, and by taking the difference between the outputs of the two photodetectors.
In these optical discs, a high recording density was achieved by improving the playback resolution of an optical pickup loaded on a reproducing apparatus. For improving the playback resolution of an optical pickup, a shorter wavelength xcex of the laser light is used for data playback or a larger numerical aperture NA of an optical lens is used for converging the laser light on the optical disc.
The wavelength xcex of the laser light used for data playback, the numerical aperture NA of the optical lens and the values of the track pitch are shown for CD, MD, MDData2, DVD-RW and DVD-ROM are shown in Table 1. It is noted that CD, MD, MDData2, DVD-RW and DVD-ROM are all trademarks for different types of the optical discs.
In a conventional optical disc, in order to achieve a high recording density, a narrow track width was realized by shortening the wavelength xcex of the laser light or by enlarging the numerical aperture NA of the optical lens, as shown in Table 1.
Meanwhile, in the conventional optical disc, the track pitch is on the order of xc2xd to ⅔ of the cut-off frequency of the optical pickup of the reproducing apparatus. The cut-off frequency herein means a frequency for which the amplitude of the playback signal is approximately 0. It is noted that the cut-off frequency is represented by 2NA/xcex, where xcex is the wavelength of the laser light used for data reproduction and NA is the numerical aperture of an optical lens used for converging the laser light on an optical disc.
The reason the track pitch is on the order of xc2xd to ⅔ of the cut-off frequency is that, for realizing stable tracking servo or track seek, it is necessary to achieve a sufficiently high level of a signal required for tracking servo or seek.
For example, in an optical disc in which information signals are of high density, push-pull signals are used as tracking error signals. If desired to achieve stable tracking servo, the amplitude ratio of push-pull signals needs to be on the order of 0.14 or higher. Also, cross-track signals are used for traverse counting in seeking and for detecting track radial positions. For stable seek, a cross track signal amplitude needs to be on the order of 0.06 or more. If, in a conventional optical disc, the amplitude ratio of the push-pull signal is to be 0.14 or more and the cross track signal amplitude is to be 0.06 or more, the track pitch has to be on the order of xc2xd to ⅔ of the cut-off frequency.
Meanwhile, a push-pull signal is obtained by detecting light reflected and diffracted by a groove by two photodetectors A, B arranged symmetrically with respect to the track center and by taking a difference (Axe2x88x92B) of outputs from the two photodetectors A and B, as shown in FIG. 1. The cross-track signals are obtained by taking the sum of outputs of these two photodetectors A and B.
The amplitude ratio of the push-pull signals is represented by C/Mmax, where C is the maximum amplitude of the push-pull signal, as shown in FIG. 2. The maximum amplitude ratio of cross-track signals is represented by D/Mmax, as shown in FIG. 2, where D is the maximum amplitude of cross-track signals and Mmax is the maximum value of a sum signal M of signals from the two photodetectors A and B, that is the value of the sum signal M on the mirror surface of the disc.
Meanwhile, in an optical recording medium, such as an optical disc, it is desired to raise the recording density of the recording signals further. To this end, it suffices to narrow the gap between neighboring grooves to narrow down the track pitch. However, if, in a conventional optical recording medium, the track pitch is too narrow, the signals necessary for tracking servo or seek cannot be obtained with a sufficient level, such that stable tracking servo or seek cannot be achieved.
For example, in MD Data2, the track pitch is 0.95 xcexcm, with the push-pull signal amplitude ratio being on the order of 0.30. In such case, the push-pull signal amplitude ratio is large to permit stable tracking servo to be achieved. However, if, in a configuration similar to that of the MD Data2, the track pitch is 0.75 xcexcm, the push-pull signal amplitude ratio is as low as approximately 0.07. This push-pull signal amplitude ratio is too low to realize stable tracking servo.
If, in a configuration similar to one of MD Data2, the track pitch is set to 0.75 xcexcm, the push-pull signal amplitude ratio is as low as approximately 0.06, while the cross-track amplitude ratio is as low as approximately 0.05. These values of the push-pull signal amplitude ratio and the cross-track amplitude ratio are to low to realize stable tracking servo or seek.
Thus, in a conventional optical recording medium, if the track pitch is too narrow, it becomes impossible to achieve signals required for tracking servo or seek with a sufficient level, such that stable tracking servo or seek cannot be achieved, with the result that, with the conventional optical recording medium, the recording density cannot be improved further.
It is therefore an object of the present invention to provide an optical recording medium, a master disc used for the preparation of the optical recording medium and an optical recording and/or reproducing apparatus for recording and/or reproducing information signals for such an optical recording medium, in which tracking servo or seek can be achieved in stability even if the track pitch is reduced to an extremely small value.
In one aspect, the present invention provides an optical recording medium in which a groove is formed for extending along a recording track and in which the light with a wavelength xcex is illuminated for recording and/or reproduction, wherein, as such groove, a first groove and a second groove are formed to a first depth to describe a double helix, and wherein a third groove having a second depth shallower than the first depth is formed between the first and second groves describing double helices.
In this optical recording medium, in which the third groove having a second depth shallower than the first depth is formed between the first and second groves describing double helices, the bottom of the third groove is substantially flat, so that optimum signals required for tracking servo and seek may be acquired.
In this optical recording medium, if a phase depth of the first and second grooves represented by xxc3x97nx/xcex, x being the first depth and nx being a refractive index of a medium from the light incident surface to the first and second grooves, is X, and if a phase depth of the third groove represented by yxc3x97ny/xcex, y being the second depth and ny being a refractive index of a medium from the light incident surface to the third groove, is Y, the first, second and third grooves are set for satisfying the equations (1) to (3) or the equations (4)and (5):
Yxe2x89xa736.9189xe2x88x92208.0190X+294.3845X2xe2x80x83xe2x80x83(1)
Yxe2x89xa7xe2x88x921.2977+8.2017Xxe2x88x9215.8226X2+12.3273X3xe2x80x83xe2x80x83(2)
Yxe2x89xa6xe2x88x92214.05681+2423.29342Xxe2x88x9210933.24673X2+24597.79851X3xe2x88x9227576.99399X4+12319.79865X5xe2x80x83xe2x80x83(3)
Yxe2x89xa7xe2x88x924.6463+30.2156Xxe2x88x9264.3100X2+47.1308X3xe2x80x83xe2x80x83(4)
Yxe2x89xa62.7669xe2x88x9220.0529X+48.0353X2xe2x88x9235.4870X3xe2x80x83xe2x80x83(5)
In this case, since the first to third grooves are formed to satisfy the above equations (1) to (3) or the equations (4) and (5), the signals required for tracking servo or seek may be acquired at sufficient levels even if the track pitch is diminished.
The first to third grooves are preferably formed to satisfy the following equations (6) and (7) or (8) and (9):
Yxe2x89xa70.8680xe2x88x927.3968X+21.8561X2xe2x88x9217.5125X3xe2x80x83xe2x80x83(6).
Yxe2x89xa6xe2x88x92261.77076+3646.50412Xxe2x88x9220988.26504X2+63944.54992X3xe2x88x92108758.21706X4+97951.29191X5xe2x88x9236518.20328X6xe2x80x83xe2x80x83(7)
Yxe2x89xa710.2606xe2x88x9260.3765X+118.5901X2xe2x88x9275.9408X3xe2x80x83xe2x80x83(8)
Yxe2x89xa6xe2x88x926.8296+29.9281Xxe2x88x9238.6228X2+14.0747X3xe2x80x83xe2x80x83(9).
24.
In this case, since the first to third grooves are formed to satisfy the above equations (6) and (7) or the equations (8) and (9), the signals required for tracking servo or seek may be acquired at sufficient levels.
Moreover, the first to third grooves are preferably formed to satisfy the following equations (10), (11) and (12):
Yxe2x89xa70.8680xe2x88x927.3968X+21.856X2xe2x88x9217.5125X3xe2x80x83xe2x80x83(10)
Yxe2x89xa736.9189xe2x88x92208.0190X+294.3845X2xe2x80x83xe2x80x83(11)
Yxe2x89xa6xe2x88x92214.05681+2423.29342Xxe2x88x9210933.24673X2+24597.79851X3xe2x88x9227576.99399X4+12319.79865X5xe2x80x83xe2x80x83(12).
In this optical recording medium, since the first to third grooves are formed to satisfy the above equations (10), (11) and (12), the signals required for tracking servo or seek may be acquired at sufficient levels.
Meanwhile, in these optical recording mediums, at least one of the first and second grooves is preferably such a wobbling groove formed so that at least a portion thereof is meandered. This allows to add the address information to no other than the grooves,
In another aspect, the present invention provides a master disc for the preparation of an optical recording medium which has a groove formed along a recording track and which is illuminated by the light with a wavelength xcex for recording and/or reproduction, wherein, as a crest-and-groove pattern corresponding to such groove, a first groove pattern and a second groove pattern are formed to a first depth to describe a double spiral, and wherein a third groove pattern having a second depth shallower than the first depth is formed between the first and second groove patterns describing double spiral.
In this master disc for the preparation of the optical recording medium, in which the third groove pattern having the second depth shallower than the first depth is formed between the first and second groove patterns of the first depth describing the double helix, the bottom surface of the third groove pattern is substantially flat. In the optical recording medium, prepared using this master disc for the preparation of the optical recording medium, in which the third groove pattern having the second depth shallower than the first depth is formed between the first and second groove patterns of the first depth describing the double helix, with the bottom surface of the third groove pattern being substantially flat, the signals required for tracking servo or seek can be optimally acquired. So, with the present master disc for the preparation of the optical recording medium, an optical recording medium may be produced in which it is possible to optimally produce signals required for tracking servo and seek.
With the present master disc for the preparation of the optical recording medium, if a phase depth of the first and second groove patterns represented by xxc3x97nx/xcex, x being the first depth and nx being a refractive index of a medium from the light incident surface to the first and second grooves, is X, and if a phase depth of the third groove pattern represented by yxc3x97ny/xcex, y being the second depth and ny being a refractive index of a medium from the light incident surface to the third groove, is Y, the first, second and third groove patterns are set for satisfying the equations (1) to (3) or the equations (4)and (5):
Yxe2x89xa736.9189xe2x88x92208.0190X+294.3845X2xe2x80x83xe2x80x83(1)
Yxe2x89xa7xe2x88x921.2977+8.2017Xxe2x88x9215.8226X2+12.3273X3xe2x80x83xe2x80x83(2)
xe2x80x83Yxe2x89xa6xe2x88x92214.05681+2423.29342Xxe2x88x9210933.24673X2+24597.79851X3xe2x88x9227576.99399X4+12319.79865X5xe2x80x83xe2x80x83(3)
Yxe2x89xa7xe2x88x924.6463+30.2156Xxe2x88x9264.3100X2+47.1308X3xe2x80x83xe2x80x83(4)
Yxe2x89xa62.7669xe2x88x9220.0529X+48.0353X2xe2x88x9235.4870X3xe2x80x83xe2x80x83(5).
In this case, since the first to third groove patterns are formed to satisfy the above equations (1) to (3) or the equations (4) and (5), it is possible to produce an optical recording medium having formed thereon the first to third grooves satisfying the above equations (1) to (3) or the equations (4) and (5) by using the present master disc for the preparation of the optical recording medium. Thus, with the present master disc for the preparation of the optical recording medium, it is possible to produce an optical recording medium in which the signals required for tracking servo or seek can be acquired at sufficient levels even with a narrow track pitch.
On the other hand, the first to third groove patterns are preferably formed to satisfy the following equations (6) and (7) or the following equations (8) and (9):
Yxe2x89xa70.8680xe2x88x927.3968X+21.8561X2xe2x88x9217.5125X3xe2x80x83xe2x80x83(6)
Yxe2x89xa6xe2x88x92261.77076+3646.50412Xxe2x88x9220988.26504X2+63944.54992X3xe2x88x92108758.21706X4+97951.29191X5xe2x88x9236518.20328X6xe2x80x83xe2x80x83(7)
Yxe2x89xa710.2606xe2x88x9260.3765X+118.5901X2xe2x88x9275.9408X3xe2x80x83xe2x80x83(8)
xe2x80x83Yxe2x89xa6xe2x88x926.8296+29.9281Xxe2x88x9238.6228X2+14.0747X3xe2x80x83xe2x80x83(9).
In the present master disc for the preparation of the optical recording medium, in which the first to third groove patterns are preferably formed to satisfy the following equations (6) and (7) or the following equations (8) and (9), an optical recording medium having formed thereon the first to third grooves satisfying the equations (6) and (7) or the equations (8) and (9) may be produced with the use of the present master disc for the preparation of the optical recording medium. Thus, with the present master disc for the preparation of the optical recording medium, it is possible to produce an optical recording medium in which the signals required for tracking servo or seek can be acquired at sufficient levels even with a narrow track pitch.
Moreover, the first to third groove patterns are preferably formed to satisfy the following equations (10), (11) and (12):
Yxe2x89xa70.8680xe2x88x927.3968X+21.856X2xe2x88x9217.5125X3xe2x80x83xe2x80x83(10)
Yxe2x89xa736.9189xe2x88x92208.0190X+294.3845X2xe2x80x83xe2x80x83(11)
Yxe2x89xa6xe2x88x92214.05681+2423.29342Xxe2x88x9210933.24673X2+24597.79851X3xe2x88x9227576.99399X4+12319.79865X5xe2x80x83xe2x80x83(12).
In the present master disc for the preparation of the optical recording medium, in which the first to third groove patterns are preferably formed to satisfy the equations (10), (11) and (12), an optical recording medium having formed thereon the first to third grooves satisfying the equations (10), (11) and (12) may be produced with the use of the present master disc for the preparation of the optical recording medium. Thus, with the present master disc for the preparation of the optical recording medium, it is possible to produce an optical recording medium in which the signals required for tracking servo or seek can be acquired at sufficient levels despite a narrow track pitch.
Meanwhile, in these optical recording mediums, at least one of the first and second grooves is a wobbling groove formed so that at least a portion thereof is meandered.
This allows to produce an optical recording medium in which at least one of the first and second grooves is a wobbling groove at least a portion of which is meandered. With the optical recording medium, thus prepared, the address information can be added to no other than the grooves.
In another aspect, the present invention provides an optical recording and/or reproducing apparatus for recording and/or reproducing the information by illuminating the light with a wavelength A on an optical recording medium having a groove formed along a recording track, wherein the optical recording medium is such a one in which, as the groove, a first groove and a second groove are formed to a first depth to describe a double helix and n which a third groove having a second depth shallower than the first depth is formed between the first and second groves describing double helices.
With the present optical recording and/or reproducing apparatus, in which a third groove having a second depth shallower than the first depth is formed between the first and second groves describing double helices, the bottom of the third groove of the optical recording medium is substantially flat to allow to produce the signals required for tracking servo or seek.
In the present optical recording and/or reproducing apparatus, if a phase depth of the first and second grooves represented by xxc3x97nx/xcex, x being the first depth and nx being a refractive index of a medium from the light incident surface to the first and second grooves, is X, and if a phase depth of the third groove represented by yxc3x97ny/xcex, y being the second depth and ny being a refractive index of a medium from the light incident surface to the third groove, is Y, the first, second and third grooves are set for satisfying the equations (1) to (3) or the equations (4)and (5):
Yxe2x89xa736.9189xe2x88x92208.0190X+294.3845X2xe2x80x83xe2x80x83(1)
Yxe2x89xa7xe2x88x921.2977+8.2017Xxe2x88x9215.8226X2+12.3273X3xe2x80x83xe2x80x83(2)
Yxe2x89xa6xe2x88x92214.05681+2423.29342Xxe2x88x9210933.24673X2+24597.79851X3xe2x88x9227576.99399X4+12319.79865X5xe2x80x83xe2x80x83(3)
Yxe2x89xa7xe2x88x924.6463+30.2156Xxe2x88x9264.3100X2+47.1308X3xe2x80x83xe2x80x83(4)
Yxe2x89xa62.7669xe2x88x9220.0529X+48.0353X2xe2x88x9235.4870X3xe2x80x83xe2x80x83(5).
Since the first to third grooves of the optical recording medium are formed to satisfy the above equations (1) to (3) or the equations (4) and (5), the signals required for tracking servo or seek can be obtained with sufficient levels, even with a narrow track pitch.
Alternatively, the first to third grooves of the optical recording medium are preferably formed to satisfy the following equations (6) and (7) or the equations (8) and (9):
Yxe2x89xa70.8680xe2x88x927.3968X+21.8561X2xe2x88x9217.5125X3xe2x80x83xe2x80x83(6)
Yxe2x89xa6xe2x88x92261.77076+3646.50412Xxe2x88x9220988.26504X2+63944.54992X3xe2x88x92108758.21706X4+97951.29191X5xe2x88x9236518.20328X6xe2x80x83xe2x80x83(7)
Yxe2x89xa710.2606xe2x88x9260.3765X+118.5901X2xe2x88x9275.9408X3xe2x80x83xe2x80x83(8)
Yxe2x89xa6xe2x88x926.8296+29.9281Xxe2x88x9238.6228X2+14.0747X3xe2x80x83xe2x80x83(9).
In the present optical recording and/or reproducing apparatus, in which the first to third grooves of the optical recording medium are formed to satisfy the equations (6) and (7) or the equations (8) and (9), the signals required for tracking servo or seek can be obtained with sufficient levels, even with a narrow track pitch.
Alternatively, the first to third grooves of the optical recording medium are preferably formed to satisfy the following equations (10) to (12):
Yxe2x89xa70.8680xe2x88x927.3968X+21.856X2xe2x88x9217.5125X3xe2x80x83xe2x80x83(10)
Yxe2x89xa736.9189xe2x88x92208.0190X+294.3845X2xe2x80x83xe2x80x83(11)
Yxe2x89xa6xe2x88x92214.05681+2423.29342Xxe2x88x9210933.24673X2+24597.79851X3xe2x88x9227576.99399X4+12319.79865X5xe2x80x83xe2x80x83(12).
In the present optical recording and/or reproducing apparatus, in which the first to third grooves of the optical recording medium are formed to satisfy the equations (10) to (12), the signals required for tracking servo or seek can be obtained with sufficient levels, even with a narrow track pitch.
Meanwhile, in these recording and/or reproducing apparatus, at least one of the first and second grooves is a wobbling groove formed so that at least a portion thereof is meandered. This enables the signals required for tracking servo or seek to be produced optimally.
Other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments thereof and the claims.